Air–sea fluxes including the effect of the molecular skin layer

A theoretical framework is presented that describes the transfer of momentum, heat and mass through the air–sea interface. It is based on the steady-state balance of turbulent kinetic energy, which allows the consistent derivation of turbulent velocity, and dissipation rate across the air–sea interface. The theory is of K – L -type with particular accuracy near the interface, which is considered to be fixed and aerodynamically smooth. Stationarity, horizontal homogeneity, and the invariance of the vertical fluxes have to be assumed. rofiles are discussed as results of numerical integration of the balance equations and as analytical two-or three-layer approximations. A wide range of field and laboratory data is used to determine four dimensionless tuning parameters. It is demonstrated how the stratification changes the wind and Schmidt number dependence of the gas transfer velocity. alistic environmental conditions, profiles of velocity, temperature and carbon dioxide concentration are presented. They extend from some height in the air through the interface down to some depth in the sea. While the major transfer resistance of momentum lies within the turbulent atmospheric layer, the temperature profile is influenced by the skin layers at both sides. The flux of carbon dioxide is mainly controlled by the skin of the ocean. During calm situations the transfer is influenced by stratification changing to exclusively molecular transports for stable stratification but to free convection for unstable stratification. For passive tracers such as carbon dioxide a corresponding parameterisation of the transfer velocity is presented.